Fuel cells to be mounted on automobiles are attracting public attention. Fuel cells of this type utilize chemical energy directly as electrical energy without converting it to thermal energy and normally generate electricity by the reaction of hydrogen with oxygen. Fuel cells are available in several types such as phosphoric acid fuel cell, solid electrolyte fuel cell and solid polymer fuel cell (PEFC) and separators that are electrically conductive molded articles are used in solid polymer fuel cells and phosphoric acid fuel cells. The separator constitutes a unit cell together with electrodes and the like and, as the unit cells are used in a layered arrangement, the separator is required to keep gases (hydrogen and oxygen) separated from each other on the one hand and to be electrically conductive on the other. For this reason, the separator must meet requirements of a high electrical conductivity of 10×10−2 Ωcm or less, low gas permeability and good resistance to oxidation, hydrolysis and hot water.
A graphitized carbonaceous material composed of a binder and carbonaceous particles of plural particle sizes is proposed in JP1992-214072 A in order to obtain a carbonaceous material that is dense, mechanically strong, electrically conductive and suitable for a fuel cell separator. This technique, however, requires graphitization after molding. A carbonaceous material formulated from a thermosetting resin, Ketjenblack and spherical graphite particles is proposed in JP1996-31231 A in order to obtain a carbonaceous material suitable for a fuel cell separator that shows a void of 5% or less and, when molded, shows a ratio of the volume resistivity in the XY direction to that in the Z direction of 2 or less. Moreover, in order to reduce the amount of binder and improve the electrical conductivity, a method is proposed in JP1999-195422 A for incorporating a small amount of binder in a carbonaceous material, molding the mixture under pressure and impregnating the molded article with an impregnating agent. Still more, a fuel cell separator whose surface roughness is controlled within the specified range to reduce contact resistance to the electrode part is proposed in JP1999-297338 A. The use of synthetic graphite together with natural graphite is proposed in JP2000-40517 A to produce a fuel cell separator with minimal anisotropy. The use of specified graphite particles is proposed in JP2000-21421 A to produce a fuel cell separator that is well-balanced in properties such as gas impermeability, thermal conductivity and electrical conductivity. There is, however, a strong demand for fuel cell separators that show better properties and are better balanced.